This project is designed to study pulmonary surfactant production in the newborn rabbit. We have previously shown that in the immediate postnatal period there is an increase in the amount of surfactant phospholipid in lung lavage. Labor increases both the initial rate of release of surfactant as well as the total amount released during the first 12 hours following delivery. We wish to determine which component of labor is responsible for the increased production of surfactant. Since it is known that circulating catecholamines are increased following labor and there is evidence that surfactant production may be under neurohumoral control, we will administer various neurohumoral agents, e.g. pilocarpine, fenoterol and isoxsurpine as well as their antagonists i.e. atropine and propranolol, to newborn rabbits at 29, 30 and 31 days following delivery by cesarean section. We will determine the effect of these agents on the phospholipid content of lung lavage. In addition we will determine the effect of these agents on a number of enzymes of phospholipid biosynthesis, since we have already shown that labor stimulates the activity of at least one enzyme-cholinephosphotransferase. In addition to these studies on whole animals we will determine the effect of pretreatment of pregnant animals with various neurohumoral agents on the release of surfactant phospholipids from slices of newborn lung. These studies should lead to a better understanding of the steps involved in production of pulmonary surfactant and its control in the newborn animal.